Semester Final Examination

Name : Melvika Anggarini
NIM   : RSA1C311010
Prodi  : Pend. Fisika PGSBI

1.      Design a simple research about the kinetic energy associated with your daily life and arrange your report in accord with the sixth science process skills you have already understood

       Yesterday, i saw my nephew threw a small rock toward his friend in front of him.  And i observed the moving of stone.  When the stone release from my nephew hand, the stone hit  the forehade of my nephew’s friend. Than I think,  to hit the forehead of my nephew’s friend, a stone need some energy. So, when  the stone threw from my nephew hands, it have a velovity to move and have energy to hit. Energy that the stone have because of its velocity called kinetic energy.

       Energy is capacity system to do work.  There are many kind of energy in this world, one of them is kinetic enrgy. Kinetic energy is the energy  in moving object or the energy that happend because of velocity an object. If we see an object with velocity v and mass m, so we can say that the kinetic energy is equals with half times the mass of the object times square the speed of the object. In symbols :

E_K = (1/2)mv²

Where :      Ek = Kinetic Energy ( Joule or J )

             m = Mass of object ( Kilogram or Kg )

        v = velocity of an object ( meter/ sekon or m/s )

So the kinetic energy is proportional to the mass of the object m and proportional to the square of the velocity. If the masses become twice the kinetic energy increase twice as well, and if speed is increased to twice the kinetic energy will increase to four times. So if we back to the problem above, if we increase the mass of stone twice, the kinetic energy will increase twice and it’s mean the stone will hurter than initial mass of stone. In other hand, if we inrease the velocity of object twice, the kinetic energy will raise twice too, so same like above,  it;s mean the stone will hurt the forehead my nephew friends more than intial velocity of stone.

Example :

How much kinetic energy does an object have if its mass is 5.0 kg and it is moving at a speed of 4.0 m/s?

Solution

Known : m = 5 kg

               V =  4 m/s

Ask        : Ek ?

Answer  : Ek = (1/2)mv²

                      = ½ x 5 kg x ( 4 m/s) ²

    Ek = 40 Joule

So, how about kinetic energy in deceelerate object?. I think a deceelerate object sill have kinetic energy because the object still have velocity but decrease. And because velocity is decreased the kinetic energy will decreased to until touching zero if velocity is zero.

2.      Describe an experiment which associated with the following terms : pendulum, frictional force and  highest point, then enter the terms into the procedures so that these terms included in your experiment.

I believe every one ever heard about constant acceleration of gravity. Constant acceleration of gravity in earth, moon, and other planet is different each other . In earth, we already know the value  constant acceleration of gravity is 9,8 m/s square or usually high school book write it is 10 m/s square. To proove the value of constant acceleration of gravity is 9,8 m/s square, we can do a simple experiment using a pendulum. In this experiment, In analyzing the simple pendulum motion, the friction force air we ignore because it will so complicated if we calculate friction force, and mass of  the rope is very negligible so we can ignore it relative to the ball. In do experiment with pendulum in highest point 15 degrees and some length of rope to take 10 swings, and calculate the result with this equation we can get constant acceleration of gravity : g = 4 phi^2 l / T

Now we will study about the experiment, check it out J

What we need?

1. Ball mattress 1 meter

2. stopwatch

3. gravel

4. arc

5. A4 paper

6. stationery

What is the procedure?

1.      Tying stone with rope

2.      Swinging a stone that has been tied to the 20-cm

3.      Observing the pendulum swings until have harmonic motion  in the  highest point is  15 degrees

4.      Counting up to 10 vibrations a stopwatch

5.      Take note of the time required for 10 vibrations

6.      Repeating the experiment from 2 to 5 with a length of rope 40 cm and 60 cm and 80 cm.

7.      Noting the results of experiments on the observation table.

8.      Calculate the constant acceleration of gravity using equation given before.

9.      Compare the value conctant acceleration of gravity known with result of experiment.

Result

The value of constant acceleration of gravity that we get from experiment is little different with the wellknown value. It may be happend because maybe there are some error in experiment, human error or instrumental error. But the result is neaar 9 – 10 m/s square.

3.      Make a simple calculation about electrical using the formula your well known. Write down your solution, and explain it by using your sentence ( change the number or symbol into your own word )

Current and charge

            We can see that when charged particles flow past a point in a circuit, we say that there is a current in the circuit. The charge flow past the point need time.  Electrical current is measured in ampere ( A ), Charged measured in Coulumb ( C ) and time measured in sekon ( s ).  So, we can get relationship between charge, current and time written as following word equation  :

            Charge = current x time

The formula written in symbol :

            delta Q = I. deltat

Where : delta Q = The amount of charge  which flows during a time interval  ( C )

              I           = Current ( A )

              delta t   = change or interval of time ( s )

From the equation above we can say that :

“One coulumb is the amount of charge which flows past a point in a circuit a time of 1 s when the current is 1 A.”

“The Amount of charge is proportional with electrical current and invers with interval of time, in higher value of electrical current and lower interval of time will produce bigger amount of charge”.

Example :

1.      There is a current of 10 A through a lamp for 1 hour. Calculate how much chrarge flows through the lamp in this time.

Solution

Known  :  I         =  10 A

               delta t  =  1 hour  = 3.600 s

Ask         : delta Q ?

Answer :  delta Q = I x  delta t 

                            = 10 x 3.600 s

               delta Q  = 36.000 C

So, in this problem the amount of charge which flows past in a circuit with current is 10 A in 1 hour is 36.000 C

2.      Calculate the current in a circuit when a charge of 180 C passes a point in a circuit in 2 minutes.

Solution

Known   :  delta Q  = 180 C

                 delta t    = 2 minutes = 2 x 60 s = 120 s

Ask         : I ?

Answer :    I = delta Q  / delta t     

                  I =  180 C / 120 s

                  I = 1,5 A

So, in this problem to make 180 C charge passes a point in 2 minutes, we need 1,5 A electric current

4. Make an essay about sound as a wave. Then show at least three evidence and examplifying about it.

Sound is one kind of wave, a longitudinal wave exactly.  Longitudinal waves are waves in which the motion of the individual particles of the medium is in a direction that is parallel to the direction of energy transport. Example of longitudinal waves are wave created in slinky and sound wave in the air. In sound wave propagation, there are “rapatan” and “ renggangan”, that made by intermediet partisles waves. When the sound waves propagating in air, intermediaries are particles in the air. Sound waves can not propagate in a vacuum because there is no air particles in the air.

Sound as  waves have properties similar to the properties of wave, such as :

a. Can be reflected (reflection)

Sound can reflect  occuring  when sound meet hard surfaces, such as stone walls  surfaces, cement, steel, glass and zinc.

example:

- Our voices will louder in the cave due to the reflection of sound on the wall of the cave.

- Our voices inside the building or music studio that does not use a silencere will louder   than in the outside

      Location of the walls of the room were too close causing reflected sound is not enough time to propagate, so that the original sound  and reflected sound heard simultaneously. This proves the reflected sound reinforces the original sound. That's why the voice in music studios louder  than outside. This explanation also same with  the situation voice in the cuve.

b. Can be refracted (refiaksi)

Refiaksi is bent  direction of path wave after passing the boundary between two different medium.

Example:  

- At night the sound of thunder sounded louder than during the day because of the   refraction of sound waves.

        During the day, the air in the upper layers colder than the bottom layer. The propagation of sound in cold temperatures is smaller than the heat. Thus, the speed of sound in the upper air layer is smaller than the speed of sound in air layer below, because the medium more dense on the top layer of the medium on the bottom layer. So, during the day, the sound of thunder travels from the upper air layers toward lower air layer would refracted away from the normal line (Figure 3.2a).

   

Figure 3.2. Refraction of sound waves

At night, the opposite happens, the air in the lower layers (near the ground) is cooler than the air on the top layer. Thus, the speed of sound in the lower layer is smaller than the upper layer, because the medium on the top layer is less dense than the medium on the bottom layer. So, at night, the sound of thunder travels from the upper air layer leading to lower air layer (denser medium) will be refracted normal line approach (Figure 3.2b). Refraction sound of thunder approaching normal line at night is what causes the sound of thunder nearer your home, and as a result you hear the thunder louder.

c. Can be combined (interference)

Same as light interference, sound interference also requires two coherent sources of sound.

Example: Two loudspeakers are connected to a signal generator (audio frequency generators) can serve as two coherent sources of sound.

          If each loudspeaker produce sound that have same fase and same deviation and placed in a distance. So the combined of two sound will produce maximum interference  Interfernce maximum can reinforce sound, so in this case, the combined two sound can produce louder sound to be source sound.

d. Can be bent (diffracted)

Diffraction is flexing sound waves when passing through a narrow slit.

Example: We can hear the sound of the room of different and closed, because the sound through narrow slits that are passable sound.

       As we se above, diffraction is flxing sound when passing narrow slit, so in this case, in the different and closed room, we still can hear voice from another room because sound can flexing through narrow slit like ventilation in the room. So because this flexing sound or diffraction process the voice from another room still we hear.

Weight or mass?

 I believe each of us see the weigh at least two months or every week?. Then when someone see their  weight and shock to see her weight go up then we'll hear "oh no, Imy weight gained 5 kg". Then when we shop at traditional markets, when order groceries we usually say, "buy chicken half kilogram weight please?". Then what's wrong with 2 sentencesabove ?. Let's look at these sentence, there are physical quantities and units of weight and kilograms. Are they the right pair of quantity and unit? Let's follow the explanation this time. :)

Magnitude is something that can measure and have  value. Magnitude divided  into two principal amount and the derrivativ quantity. The amount of the principal amount of a unit is determined before. There are  7 scale that is included in basic quantity :

1. Length (l) with units of meters (m)

2. Mass (m) with unit Kilogram (kg)

3. Time (t) with units of seconds (s)

4. Strong Flow (i) the unit Ampere (A)

5. Temperature (T) and Kelvin (K)

6. The light intensity (I) with unit Candela (Ca)

7. The number of units Molukel with Mole (mol)

Furthermore, the magnitude of the derivative is the amount of other quantities are derived from the principal amount. Inordinate amount of derivatives in their daily lives, for example, such as weight (N), velocity (m / s), pressure (Pa), dlll. As we saw above, both the principal amount and the amount of its derivatives have the units of each,. We can not pair with a long second unit.

Well, from the explanation above, we can see the error on our daily two statements above. Apparently nit of weight  not kilogram but newtons, and quantity  that has the unit of mass is the kilogram. So now we know that we  calculate everyday  is the masses who have the units of kilograms and is one of the principal amount of members, not weight.

We can express the amount  of weigh it , but we have to adjust again the value and units. Weight is the gravitational constant mass multiplication of objects. So the weight of the object may change change if the value of the acceleration of gravity changes. The formula weight is:

W = m x g

With w (N) is the weight, m ​​(kg) is the mass and g (m / s squared) is the acceleration of gravity. For example, we consider our mass of 45 kg, berapkah weight if known gravity 9.8 m / second squared?

W = m x g

W = 45 kg x 9.8 m / s squared

W = 441 N

From the calculation above  we can say that the weight of us is  441 N. But this value will change if we were on the moon, because the moon's gravitational constant value different from the earth. So the value of 441 N and is only valid if it is measured on earth.

So, the conclusion is weight is different from masss, because weight depend on gravitational constant and mass is constant. And remember 45 kg is not your weight but your mass.

Furthermore, let's prediction, how heavy an object if we take it to a vacuum?. I think a body would have the different weight values ​​as well as the vacuum has an individual value of the gravitational constant. Let us remember that the vacuum is a room with no air, not space without gravity, so the vacuum still have the value of the gravitational constant and can be calculated by weight.

Hope ituseful :)

Calculating Acceleration

The meaning of acceleration     

In everyday language, the term accelerating means “ speeeding up “. Anything whose speed is increasing is accelerating. Anything whose speed is decreasing is decelarating. To be more precisi in our definition of acceleration, we should think of it as changing of which is changing its direction has acceleration. Because acceleration is linked to velocity in this way, it follows that is a vector quantity. Example of objects acceerating is A car speeding up as it leaves the town, the driver presses on the accelerator pedal to increase the car’ velocity.

Calculating acceleration

          The acceleration of something indicates the rate at which its velocity is changing.  Languange can get awkward here. We might say “ the sprinter accelerates faster than the car”. However, “faster” really means “greater speed”. So it is better to say  “ the sprinter has a greater acceleration than the car. Acceleration is defined as follows :

                   Acceleration = rate of change of velocity

                   Acceleration =  Change in velocity / time taken

                                                

So to calculate accelaration a, we need to know two quantities, the change of velocity  delta v and time taken delta t.

                   a = v / t

Sometimes this equation is writte differently. We write u for the initial velocity and v for the final vlocity ( because u comes before v in the alpabet). The moving object accelarates from u to v in a time t ( this is the same as the time rpresented bg delta t above). The accelerationis given by the equation :

                   a = v – u / t

                           

Example

1.     Leaving a bus stop, the bus reaches a velocity of 8.0 m/s after 10 s. Calculate the accelaration of the bus.

Step 1 : Note the bus initial velocity is 0 m/s. Therefore :
             change in velocity ( delta v ) = ( 8.0 - 0)m/s

             Time taken ( delta t ) = 10 s

Step 2 : Subtitute these values in the equation for acceleration :

              acceleration a = delta v/ delta t = 8.0 / 10 = 0.8 m/s square     

2.    A sprinter starting from rest has an acceleration of 5.0 m/s square during the first 2.0 s of race. Calculate her velocity after 2.0 s.

Step 1 : Rearranging the equation a = v - u / t , gives : v = u + at

Step 2 : Subtituting the values and calculating gives :

              V = 0 + ( 5.0 x 2.0 ) = 10 m/s

Hope it usefull :)

Playing Magic with Magnet

I believe every one in this world ever heard magnets. As we know magnet can inerect with another things by touching them. Can  magnets interact without touching the object? Scientists have try it  through air, water, glass, and other objects. Now we will study how can it happend? Check it out J

What You Need?

1.A bar magnet or magnet U

2. Paper Clip

3. Iron Powder or other metal objects from

4.Scotch Tape

5. Paper

6. Glass

7. Water

8. String

Try These:

1.     Tie the paper clip to the end of the string. Then attach the other end of the string with tape on the table or floor. Slowly lift the magnet towards the paperclip until it attracted. Be careful, do not get stuck the magnet to paper clips. Then try lifting magnet upwards slowly, try keep the distance of paper clip and magnet distance is always the same, whether the paper clips will be brought up to follow the magnet?

2.     Place the iron powder into the glass. If no try to find objects made of iron like a nail. After that, hold the magnet from the outside of the glass. Is there iron  in a glass could be attracted by a magnet?

3.   Now, pour water into the glass containing iron powder earlier. Then try to hold the magnet from outside the glass. This time the iron powder is attracted by a magnet? When finished, discard the water and pat dry with a tissue iron powder to avoid rusting.

Result

1.     The paper clips will brought up to follow the magnet

2.    Iron in the glass attrached by magnet

3.    Iron in the glass still attrached by magnet

Facts about Magnets:

After the experiment, we can see the magnets can attract objects made ​​of iron, even though there are medium such as air, water, paper, and glass. So the magnet can attract iron without direct contact with the iron. But the medium is not too thick for small magnet.

Hope it useful :)

Why when we turn off the televison the lamp still on?

Have you ever torn off one lamp in your house? What happend to other lights lamp? Is it turn off too?. The answer is no, the other lamp will not turn off too. Why it can be happend?, it is because our electricity in home using parallel circuit. To make you easier understand this concep, now i will give you a small experiment to proove that, check it out  :).

Required materials : 1. Two flashlight bulbs with sockects

                               2. Dry cell

                               3. Half a meter copper wire

                               4. Switch

                               5. Scissor

Step by step procedure :

1.    Cut the wire into five parts by scissor. Then strip about ¹/₂ inch (1.25 cm) of insulation from each end of the wires.

2.    Attach a wire to the positive side of the dry cell and connect the other end to the left side of a light bulb

3.    Attach another wire to the negative side of the dry cell and connect it to the switch

4.    Get another wire and conncet to the switch to the right side of the light bulb

5.     Add one more bulb to the setup by connect another wire to the left side of the first bulb and connecting the other end on the left side of the second bulb

6.    Connect another wire to the right side of the first bulb and connect it to the right side of the second bulb. Caution : Do not leave the wires on the screws for more than 5 to 6 seconds. The bare wire and lamp can get hot enough to burn you. Allow them to cool before touching them. The circuit  picture :

7.    See what happend when to the fiirst bulb when the second bulb added.

Result:

The adding of the second bulb is not affect to the brightness of the first bulb. The connection was not broken, the first buln is still on and light.

Why?

The electric current has more than one path to follow through the connected lamps in this experiment, so the circuit formed what is called a parallel circuit. The arrows in the electrical schematic in Figure 18.2 indicate the movement of the current (e') away from the negative terminal of the battery through the bulbs, then back to the positive terminal of the battery. At junction A (one of the screws on the side of lamp base 1), the current divides before moving through the lamps. Then the current recombines at junction B (one of the screws on the opposite side of lamp base 1) and returns to the positive terminal of the battery. The facts that the lamps are identical and glow with equal brightness show that the same amount of current reaches both lamps. This way, it is better than series circuit since the devices can be switched on and off separately without breaking any circuits and best circuit at home.